Hadoop-streaming : Reduce Task In Pending State Says "No Room For Reduce Task."

My map task completes successfully and I can see the application logs, but reducer stays in pending state Kind % Complete Num Tasks Pending Running Complete Killed Fail

Solution 1:

Your disk on the host where the reducer is run is too small. Your reducer input takes approx. 172 gbs, but you have only 63gb free.

Maybe combiner could be useful for you. Have a look here: http://tumblr.mobocracy.net/post/6589143971/using-a-combiner-with-hadoop-jobs